Let's get to the latest. Brian ross on the scene in boston. Good morning. Reporter: Good morning, george. Overnight, authorities told abc news that 19-year-old dzhokhar tsarnaev has now begun to answer questions. There's a team of federal agents trying to find out if there is an ongoing threat. The answers coming in in writings because of serious wounds he suffered. As police and federal agents closed in, after a resident reported there was a goody person hiding in his boat. A helicopter reported these images. He just sat up. He's moving and flailing about, quite a bit of movement. Reporter: The orders went out to do everything to capture the 19-year-old alive. After an initial exchange of gunfire. All unites, do not return the fire. If they're able to successfully rip that off, he'll be fully exposed. Reporter: Then they used flash-bang stun ge nads. He had been injured in a g gunfight the night before. He was ordered to surrender and he meekly pulled up his shirt to show that he was not wearing a suicide vest. The cheers went out down the street and across the country. As troubles questions about him and his older brother remains. Why did young men who grew up and studied here, as part of our communities, and our country, resort to such violence? Reporter: Nowhere were there nor questions than the nearby college campus where the 19-year-old tsarnaev was known as just another pot-spomoking student. He didn't seem like a bad guy. He was a little bit of a -- i guess a drug gugie. He just walked past me. We had a brief conversation. I asked him for a ride home. He told me, yeah. Reporter: Another friend asked him about the bombing. I talked to him about it. He was like, yeah, man, trage tragedies happen all thetime. Reporter: The night after the bombing, he sweeted I'm a stress free kind of guy, as if nothing at all had happened. Federal authorities expect to file formal criminal charges today, including counts that could lead to the death penalty. That ultimate decision left to the attorney general eric holder.

This transcript has been automatically generated and may not be 100% accurate.

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